Dye-doped silica nanoparticles are widely used in fields of biology, medicine and theoretical research on photo-physical chemistry and so on. Various properties of silica can be improved by doping it with fluorescent dyes: dyes fixed in the media of silica can be isolated from solvents and oxygen so that its dispersibility and optical stability can be improved (Nano Letter 2005, 15, 113-117); the microenvironment of dyes can be changed by adjusting the particle structure of silica so as to improve the luminescent efficiency and service life (Chem. Mater., 2008, 20, 2677-2684); and SiO2 is innoxious, chemically inert, prone to be surface functionalized, so as to expand the applied range of fluorescent dyes.
There is an urgent technical problem needs to be solved, that is realizing doping dye molecules inside the silica particles stably without any leakage. Van Blaaderen et al. use silane coupling agent (Langmuir 1992,8,2921-2931; J Colloid Interface Sci. 1993, 156, 1-18; Nano, Lett. 2005, 5, 113-117) to anchor the dye molecular inside the silica nanoparticles by means of covalent coupling method. The method requires the dye molecular have functional groups reacting with silane coupling agent, which reduces the types of doped dyes to a limited number, therefore is not universally applicable. Rosenzweig et al. utilize electrostatic interactions (Langmuir 2005, 21, 4277-4288), so as to realize doping positively charged dyes inside silica. However, because silica media carries negative charges, the method is not suitable for negatively charged dyes.
Positively charged polyelectrolyte can be both absorbed on the surface of silica and filled into the pore canal of mesoporous silica material. The nanoparticles of silica modified by positively charged polyelectrolyte can absorb negatively charged dyes, which makes silica have specific optical performances (Chem. Mater. 2008, 20, 848-858), and widely applied in the research of photophysics (J. Am. Chem. Soc. 2000, 122, 5841-5848) and photochemistry (Mater. Res. Bull. 2009, 44, 306-311) of the dyes. However, the particles of SiO2 merely act as carriers and can not protect dyes.